lens-rs

lens implemented in rust

• the Review optics describes how to construct a single value.
• A Traversal can access the multiple substructures.
• A Prism can access the substructure may exist.
• A Lens can access the substructure must exist.

Example

access the substructure ```rust fn test() -> Option<()> { let mut nested: ResultOk.Ok).review((1, 2)); *optics!(Ok.Ok.0).pmmut(&mut nested)? += 1; asserteq!(optics!(Ok.Ok.0).pm(nested)?, 2);

let mut x = (1, (2, (3, 4)));
*optics!(_1._1._1).view_mut(&mut x) *= 2;
assert_eq!(optics!(_1._1._1).view(x), 8);

let mut x: (_, Result<_, ()>) = (1, Ok((2, 3)));
*optics!(_1._Ok._1).pm_mut(&mut x)? *= 2;
assert_eq!(optics!(_1._Ok._1).pm(x)?, 6);

let mut x = (1, vec![Some((2, 3)), None]);
optics!(_1.Mapped._Some._0)
    .traverse_mut(&mut x)
    .into_iter()
    .for_each(|i| *i += 1);
assert_eq!(optics!(_1.Mapped._Some._0).traverse(x), vec![3]);

Some(())

} ```

derive lens for data types ```rust use lens_rs::*;

[derive(Review, Prism, Debug)]

enum AnEnum { A(T, i32), #[optic] B(T), }

[derive(Optic, Lens, Debug)]

struct Foo { #[optic] a: i32, #[optic] b: i32, }

fn test() -> Option<()> { let x = optics!(Some.B).review(Foo { a: 3, b: 2, }); asserteq!(optics!(_Some.B.b).pm(x)?, 2);

Some(())

} ```

assume a type T may have substructure that the type is i32. ```rust fn bar>(t: &mut T, pm: Pm) { pm.pm_mut(t).map(|x| *x += 2); }

fn test() { let mut complex = (1, Ok((Err(2), 3))); bar(&mut complex, optics!(0)); bar(&mut complex, optics!(1.Err)); // do nothing bar(&mut complex, optics!(1.Ok.0.Ok)); // do nothing bar(&mut complex, optics!(1.Ok.0.Err)); bar(&mut complex, optics!(1.Ok.1)); assert_eq!(complex, (3, Ok((Err(4), 5)))); } ```

assume a type T must have a field .a. ```rust fn withfielda(t: T) -> String where field![a]: Lens { optics!(a).view(t) }

let foo = Foo { a: "this is Foo".tostring(), b: () }; let bar = Bar { a: "this is Bar".tostring(), c: 0 };

println!("{}", withfielda(foo)); println!("{}", withfielda(bar)); ```